Tillage and residue management effects on temporal changes in soil organic carbon and fractions of a silty loam soil in the <scp>N</scp> orth <scp>C</scp> hina <scp>P</scp> lain

Soil degradation and associated depletion of soil organic carbon ( SOC ) have been major concerns in intensive farming systems because of the subsequent decline in crop yields. We assessed temporal changes in SOC and its fractions under different tillage systems for wheat ( T riticum aestivum L .) – maize ( Z ea mays L .) cropping in the N orth C hina P lain. Four tillage systems were established in 2001: plow tillage ( PT ), rotary tillage ( RT ), no‐till ( NT ), and plow tillage with residues removed ( PT 0). Concentrations of SOC , particulate organic carbon ( POC ), non‐ POC ( NPOC ), labile organic carbon ( LOC ), non‐ LOC ( NLOC ), heavy fraction carbon ( HFC ) and light fraction carbon ( LFC ) were determined to assess tillage‐induced changes in the top 50 cm. Concentrations of SOC and C fractions declined with soil depth and were significantly affected by tillage over time. The results showed that SOC and its fractions were enhanced under NT and RT from 0 to 10 cm depth compared with values for PT and PT 0. Significant decreases were observed below 10 cm depths ( P &lt; 0.05) regardless of the tillage system. The SOC concentration under NT for 0–5 cm depth was 18%, 8%, and 10% higher than that under PT 0 after 7, 9, and 12 yr of NT adoption, respectively. Apparent stratification of SOC occurred under NT compared with PT and PT 0 for depths &gt;10 cm. All parameters were positively correlated ( P &lt; 0.01); linear regressions exhibited similar patterns ( P &lt; 0.01). Therefore, to maintain and improve SOC levels, residue inputs should be complemented by the adoption of suitable tillage systems.